Media asking to render, with no reason. FCP 7.03

I have come into a project to color correct it, within FCP 7.03
The media is on an external hard drive, and the project on the mac desktop (iMac 21 inches, 12 GB ram).
After applying an effect to ONE clip of the sequence, all other clips in sequence are asking also for render, although they not only have NO effects and NO motion adjustments, and are exactly the same codec and format as the sequence (1080p24 ProResHQ).
Very strange indeed, and now every other previous project using the same media also asks for render, as if the media were not the same format as the sequence, or as if it had effects applied... !

As a test, I openend the project on another Mac, and it does not ask for such renders, so it seems like something of FCPs preferences or the iMac's RAM or something. I restarted the mac twice but nothing came of that. No other programs are running either...